The present invention relates to a sprocket for a power transmission device of a winding type to transmit power or any other force through a chain. More particularly, the present invention relates to a sprocket having a reduced volume, weight or the like by using material for a thin plate or the like, that can realize an appropriate engagement of the sprocket with a chain by bringing the position of the sprocket into agreement with the position of the chain, and that can prevent an occurrence of a flat curvature or warp upon hardening.
Generally, a transmission unit of a winding type using a chain and a sprocket has been adopted for extensive use in a power transmission system of motorcycles, bicycles or industrial machines. The shapes and sizes of the chain and the sprocket for use in this transmission unit are specified and defined as JIS (Japanese Industrial Standards) B1801.
As conventional sprockets, there is provided, for example, a normal sprocket product as shown in FIG. 32(a). This drawing (FIG. 32(a)) depicts a sectional view of a side portion of a normal sprocket product, a sectional view of the sprocket on a longitudinally central plane extending through and over the center of the sprocket, when looked at from direction A and from direction B, a sectional view of the side portion thereof when mounted on a wheel, and a sectional view of the side portion thereof showing a status of warp upon hardening the sprocket. FIGS. 32(b) and 32(c) depict the same illustrations for different sprocket products. In the drawings, a hatched portion in each of the sectional view of the side portions and the sectional view on the longitudinally central plane indicates the presence of material or a member.
As shown in FIG. 32(a), the conventional sprocket product can be mounted on a wheel in a state in which the bottommost end surface (or the uppermost end surface) of the sprocket is engaged with the surface of a flange of the wheel. Therefore, the position of the sprocket is brought into agreement with the position of the chain upon mounting on the wheel, so that the teeth sections of the sprocket can be engaged with the chain in an appropriate fashion. Further, as the upper half portion and the lower half portion of the sprocket from the longitudinally central plane are symmetrical with each other with respect to the longitudinally central plane, the sprocket can present the advantages that it does not cause or causes little warp or curving upon hardening for improving durability.
For the conventional sprocket product as shown in FIG. 32(a), however, it suffers from the defects that it is heavy and expensive in cost of production for the sprocket due to high costs for material because it is filled in with such material over the entire area extending from the bottommost end surface to the uppermost end surface, simply excluding hole portions. In order to render the sprocket lightweight, it is considered as a matter of course to render the entire area of the sprocket thinner. On the other hand, a chain engageable with the sprocket is configured such that two sheets of a pin ring plate and a roller ring plate are disposed alternately, which are disposed parallel to each other and they are mechanically connected to each other with pins. Therefore, the acceptable tensile strength of the chain has its own limits. If a chain having a narrower width than the one currently in use would be used, their may be problems with strength of the chain. The sprocket, however, has no mechanical connecting portion therein. Moreover, it has recently been proposed that the sprocket be made of material having high strength and rigidity. In this case, even if the thickness of the sprocket is half of that of the conventional sprocket, substantially the same strength and rigidity can be achieved as a sprocket prepared by using conventional material.
It is further proposed to provide a sprocket, as shown in FIG. 32(b), which is depressed on upper and lower sides and is provided with a corrugated section having an amplitude in the thickness direction at the outer peripheral part of the sprocket and further with teeth at least at the outer edge portions of the top fold parts of the corrugated section (Laid-open Japanese Patent Application No. 8-214,529). This sprocket can dramatically reduce an amount of material to be used for the production of the sprocket and, even if the material would be used in an amount of from a half to one third the conventional sprocket made of a conventional material, the sprocket can achieve substantially the same strength as the conventional sprocket. Moreover, the teeth formed on the corrugated section are disposed alternately in the thickness direction, so that the sprocket can be used in combination with a chain having a conventional width. Furthermore, as the upper half portion and the lower half portion of the sprocket are symmetrical to each other with respect to the longitudinally central plane extending through and over the center of the sprocket, the sprocket can sustain the advantages that no or little warp or curvature may be caused upon hardening.
When the sprocket in this configuration is mounted on an existing wheel, however, the mounting surface at which the sprocket is mounted on the wheel is located above the bottommost end surface of the corrugated section, as shown in FIG. 32(b). Therefore, a new problem may arise that the position of the sprocket is not brought into agreement with the position of a chain.
In order to solve this problem, it is considered to provide a sprocket with one side depressed therein, as shown in FIG. 32(c), in which its mounting surface for mounting on the wheel is thinned, like in the embodiment shown in FIG. 32(b). In this configuration, the sprocket is configured such that the mounting surface of the sprocket for mounting on the wheel can be brought into agreement with the bottommost end surface of the sprocket by placing the mounting surface of the sprocket eccentrically toward one side with respect to the longitudinally central plane extending through the center of the sprocket. Therefore, this configuration can bring the position of the sprocket into agreement with the position of the chain upon mounting on the wheel.
For the sprocket as shown in FIG. 32(c), however, the material is distributed in an asymmetrical manner with respect to the longitudinally central plane extending over and through the center of the sprocket. This asymmetrical distribution of the material over he sprocket may cause warp or curving during the hardening process, and these defects may eventually lead to disagreement of the position of the sprocket with the position of the chain.
In order to solve the problems as specifically set forth under the above description of the background technology as shown in FIGS. 32(a) to 32(c), the present invention has the object to provide a sprocket that can reduce volume and weight by using material for use in preparing thin plates or the like, that can realize an appropriate state of engagement of the sprocket with a chain by agreeing the position of the sprocket with the position of a chain, and that causes no or little warp or curving on a surface of the sprocket upon hardening the sprocket.
In order to achieve the object, the present invention provides a sprocket comprising at least a mounting part for mounting on a rotary member and an outer peripheral part at which teeth engageable with a chain are formed, wherein the mounting part comprises a first raised section raised toward a first plate surface side and a second raised section raised towards a second plate surface side opposite to said first plate surface side. The term xe2x80x9crotary memberxe2x80x9d referred to herein is intended to mean any rotary member that can transmit a drive force through a chain, when the sprocket is mounted on the rotary member. Such a rotary member includes, for example, a wheel for use with two-wheel vehicles, bicycles, motorcycles, and so on.
In accordance with the present invention, the sprocket is provided with the mounting part for mounting on a rotary member, in which the first section is raised on the one plate surface side and the second section is raised on the opposite plate surface side. Therefore, when the sprocket is mounted on the rotary member in a state that the top portion of either of the first raised section or the second raised section is engaged with a mounting plane of the rotary member, the position of the sprocket can agree with the position of the chain by adapting the height of the top portion to the position of the chain. This configuration can realize an appropriate engagement of the teeth of the sprocket of the resent invention with the chain.
Should the present invention be applied to the position relationship of the sprocket with the chain as shown in FIG. 32(a), the top portion of the first and second raised sections on the side that engages with the mounting surface of the rotary member is formed as a plane that defines the bottommost end surface of the sprocket as a whole. In this configuration, the top portion of the raised sections on the side that does not engage with the mounting surface thereof can be formed so as to define the uppermost end surface of the, sprocket as a whole. Moreover, it is to be understood as a matter of course that the top portion of each of the first and second raised sections may be disposed on a level with the bottommost end surface and the uppermost end surface of the outer peripheral part. It is to be noted herein that the top portion of each section is preferably flat and the section of the sprocket engageable with the mounting surface of the rotary member may be provided at any appropriate location with a mounting hole through which the sprocket is engaged with the rotary member.
In accordance with the present invention, the first and second raised sections are raised on the respective plate surface sides without rendering the material eccentric toward one plate surface side only, unlike a conventional sprocket product with one side depressed therein as shown in FIG. 32(c). Therefore, the sprocket can lessen an occurrence of warp or curving due to hardening because the material is equally distributed therein, as compared with the conventional sprocket product.
Furthermore, the sprocket according to the present invention is configured such that the first raised section is depressed relatively on the plate surface side corresponding to the other plate surface side toward which the second raised section is raised. Conversely, the second raised section is depressed relatively on the plate surface side corresponding to the one plate surface side toward which the first raised section is raised. This configuration can reduce the volume of the mounting part of the sprocket leading eventually to a reduction in the weight of the sprocket. Further, for instance, this configuration can render the plate thickness of the material of the mounting part smaller than the entire thickness of the outer peripheral part with the teeth formed thereon so as to adapt to a width in which it is engaged with a chain having an ordinary tooth width. Therefore, the total volume and the total weight of the sprocket can be reduced, as compared with the conventional sprocket product disclosed under the background technology (as shown in FIG. 32(a)), in which the mounting part is formed in the same plate thickness as that of the outer peripheral part as a whole. Moreover, the sprocket can further be rendered lighter in weight by locating a hole in the mounting part that extends over its entire thickness.
In accordance with the present invention, the mounting part of the sprocket is preferably configured such that the first raised section is raised toward the one plate surface side with respect to the longitudinally central plane of the sprocket extending through the center of the sprocket and the second raised section is raised toward the other plate surface side with respect to the longitudinally central plane thereof, so as to render the total volume and weight of the sprocket substantially equal between the first raised section and the second raised section. It is to be noted herein that the longitudinally central plane referred to herein is intended to mean a plane that passes through the center of the sprocket in the plate thickness direction perpendicular to the central axis of the axial direction of the sprocket.
By forming the first and second raised sections so as to divide the total volume and weight of the sprocket into substantially equal sections with respect to the longitudinally central plane, an occurrence of warp or curvature upon hardening can be reduced more effectively. Actually, as no or little warp or curvature is caused to occur upon hardening in this case, it is possible to cause the position of the sprocket to thoroughly agree with the position of the chain even after hardening.
The first and second sections can be formed in an optional and appropriate manner within the scope that does not depart from the scope and spirit of the invention. For instance, the first and second sections may each be formed in a plurality or disposed alternately with each other along the peripheral direction. Further, the mounting parts may be disposed so as to become symmetrical to each other with respect to the rotation at a predetermined angle about the central axis of the sprocket. In this instance, the first and second sections are substantially identical in shape with the exception that the plate surface sides toward which they are raised are disposed opposite to each other. Furthermore, the number of the first sections may be identical to the number of the second sections. The sprocket can be prepared with extreme ease in such a shape that the total volume and weight of the sprocket is divided substantially equal with respect to the longitudinally central plane extending through the center of the sprocket by rendering the mounting parts symmetrical to each other by rotation about the central axis of the sprocket. Moreover, this configuration can further reduce an occurrence of warp and curvature upon hardening.
Forming the sprocket as a whole with material having a uniform plate thickness can also attain a further decrease in weight of the sprocket. For instance, the sprocket can be prepared in various shapes with extreme ease by press-processing a circular plate having a uniform plate thickness.
For instance, should the sprocket be rendered lightweight by using material having a plate thickness smaller in width than the width of engagement with the chain, an appropriate state of engagement of the teeth of the sprocket with the chain can be realized by forming the outer peripheral part in the manner as will be described hereinafter. This configuration can also sustain the strength of the chain as well as render the sprocket lightweight.
For instance, the corrugated section having amplitude in the thickness direction is formed at the outer peripheral part along the peripheral direction, and teeth are formed at least at the outer edges of the top portions of the folds of the corrugated section. In this configuration, a pitch of at least one fold of the corrugated section between the top portions thereof is set to be different from a pitch of another fold of the corrugated section between the top portions thereof. In this instance, it is also possible to prepare a sprocket with an odd number of teeth by forming the teeth at an outer edge of the top portion and at an outer edge in an intermediate position of the folded portion between the top portions thereof.
Moreover, the outer peripheral part of the sprocket may be provided at its peripheral portion with the corrugated section having annular folds extending along the peripheral direction and having amplitude in the thickness direction, and teeth may be provided at the peripheral portion of the corrugated section. In addition, thick portions and thin portions may be alternately formed at the outer peripheral part along the peripheral direction and teeth may be formed on outer edge portions of the thick sections. Further, the outer peripheral part of the sprocket may be configured such that each tooth formed at the outer peripheral portion may be provided with two tooth edge portions facing each other in the thickness direction and a groove extending inside in the radial direction may be provided between the two tooth edge portions.
At the outer peripheral part provided with the corrugated section and so on may be disposed a buffer member for use with the object to reduce noises that may be caused by contact with the chain. This can attain a further effect that noises can be reduced.
It is further to be noted herein that the present invention is not restricted to the provision of the corrugated section at the outer peripheral part of the sprocket. For instance, the sprocket of the present invention may be prepared such that the outer peripheral part is made of material having a conventional plate thickness (FIG. 32(a)) and only the mounting part is made of material having a thinner plate thickness.